1. Field of the Invention
The present invention relates generally to bipolar devices and methods of making such structures. The present invention also relates to self-organizing devices, and more particularly to combinations of materials that can spontaneously form networks resulting in bipolar devices, and methods thereof.
2. Description of the Related Art
Rechargeable batteries enjoy an enormous and constantly growing global market due to their implementation in, for example, cellular telephone, laptop computers and other consumer electronic products. In addition, the development of electrically powered vehicles represents an immense potential market for these batteries.
The lithium rechargeable battery is an attractive technology due to its comparatively high energy density, low potential for environmental and safety hazard, and relatively low associated materials and processing costs. The lithium battery is charged by applying a voltage between the battery's electrodes, which causes lithium ions and electrons to be withdrawn from lithium hosts at the battery's cathode. Lithium ions flow from the cathode to the battery's anode through an electrolyte to be reduced at the anode, the overall process requiring energy. Upon discharge, the reverse occurs; lithium ions and electrons are allowed to re-enter lithium hosts at the cathode while lithium is oxidized to lithium ions at the anode, an energetically favorable process that drives electrons through an external circuit, thereby supplying electrical power to a device to which the battery is connected.
Currently known cathode storage compounds such as LiCoO2 and LiMn2O4 when used with currently known anodes such as lithium metal or carbon have working voltages between 3 and 4V. For many applications a high voltage and low weight are desirable for the cathode as this leads to high specific energy. For example, for electrical vehicle applications the energy-to-weight ratio of the battery determines the ultimate driving distance between recharging.
Cathodes in state-of-the-art rechargeable lithium batteries contain lithium ion host materials, electronically conductive particles to electronically connect the lithium ion hosts to a current collector (i.e., a battery terminal), a binder, and a lithium-conducting liquid electrolyte. The lithium ion host particles typically are particles of lithium intercalation compounds, and the electronically conductive particles are typically made of a substance such as a high surface area carbon black or graphite. The resulting cathode includes a mixture of particles of average size typically on the order of no more than about 10 to 30 microns.
Anodes for rechargeable lithium-ion batteries typically contain a lithium host material such as graphite, electronically conductive particles to electronically connect the lithium ion hosts to a current collector (i.e., a battery terminal), a binder, and a lithium conducting liquid electrolyte. Alternatives to graphite or other carbons as the lithium ion host have been described by Idota et al., in Science 1997, 276, 1395, and by Limthongkul et al., in “Nanocomposite Li-Ion Battery Anodes Produced by the Partial Reduction of Mixed Oxides,” Chem. Mat. 2001.
In such cathodes or anodes, for reliable operation, good contact between particles should be maintained to ensure an electronically conductive pathway between lithium host particles and the external circuit, and a lithium-ion-conductive pathway between lithium host particles and the electrolyte.
A solid polymer electrolyte is used as the ion conduction medium between the anode and cathode in some applications. A typical solid polymer electrolyte is composed of polymers having electron-donating atoms such as oxygen, nitrogen and phosphorus, together with a complex of lithium salt. Armand et al., in “Fast Ion Transport in Solids”, P. Vashishta, J. N. Mundy and G. K. Shenoy, Eds., North-Holland, Amsterdam (1979), p. 131, describe the use of poly(ethylene oxide) and other polyethers doped with various alkali metal salts as solid polymer electrolytes for battery applications. Subsequently, a great variety of ionically conductive solid polymer electrolytes based on a variety of lithium-ion complexing polymers have been reported (see, e.g., F. M. Gray, “Solid Polymer Electrolytes: Fundamentals and Technological Applications”, VCH, New York (1991)). More recently, detailed performance characteristics of an all-solid-state LixMnO2/Li polymer battery system were reported by Sakai et al., in the Journal of Electrochem. Soc. 149 (8), A967 (2002).
The ion conductivity of the solid polymer electrolyte is usually increased as the segmental motion of the polymer chain in increased. Therefore, the crystalline region within the polymer structure has to be minimized to increase the non-crystalline regions. Furthermore, linear or branched solid polymer electrolytes demonstrate poor mechanical properties. The mechanical properties of the polymer are shown to improve when the polymer chains are crosslinked.